1. Field of the Invention
The present invention relates to a stepping motor control circuit and an analogue electronic timepiece using the stepping motor control circuit.
2. Description of the Related Art
In the related art, a stepping motor including a stator having a rotor storage hole and a positioning device which determines the stop position of the rotor, a rotor disposed in the rotor storage hole, and a coil, and being configured to rotate the rotor by supplying an alternating signal to the coil to generate a magnetic flux in the stator and stop the rotor at a position corresponding to the positioning device is used in an analogue electronic timepiece or the like.
As a control system of the stepping motor, a correction drive system configured to detect whether the stepping motor is rotated or not when the stepping motor is driven with a main drive pulse, by detecting a detection signal on the basis of an induced voltage generated in the stepping motor and, depending on whether or not the stepping motor is rotated, changing the main drive pulse to a main drive pulse having a different pulse width for driving, or rotating the stepping motor forcedly by a corrective drive pulse having a larger pulse width than the main drive pulse is used (for example, see Patent Document JP-B-61-15385).
According to Patent Document JP-A-57-17884, a drive control of the stepping motor is performed in two segments of the induced voltage, and in one of these two segments (a segment in earlier time), control to move the rank of the pulse downward is performed for a detected voltage according to the two pulse states. In the later segment, determination of the rotation of the rotor is performed.
The pulse-down is performed when the earlier pulse is lower than the detected voltage and the later pulse is higher than the detected voltage. Also, the pulse detection time for the pulse-down control is changed regularly, so that the load variations are detected and sensed at regular intervals.
According to Patent Document WO2005/119377, when detecting the rotation of the stepping motor, a unit for comparing and discriminating a detected time and a reference time in addition to the detection of the detection signal is provided and, if the detection signal is lower than a predetermined reference threshold voltage Vcomp after having rotated the stepping motor with a main drive pulse P11, a corrective drive pulse P2 is outputted and a main drive pulse P1 for the next time is changed to a main drive pulse P12 having a large energy than the main drive pulse P11 for driving. When the detection time when rotating the rotor with the main drive pulse P12 is earlier than the reference time, the main drive pulse P12 is changed to the main drive pulse P11, and the rotation is made with the main drive pulse P1 according to a load during the drive, so that the current consumption is reduced.
However, when the eccentricity of the rotor or the displacement between the center of rotation of the rotor and the center of the stator hole is significant due to the variations in mass production, one of detent torques (torques to maintain the rotor at the initial position) for the rotor polarities corresponding to an first terminal OUT1 and a second terminal OUT2 of a drive coil becomes high and the other one becomes low.
Therefore, the present inventions in the present inventions disclosed in Patent Documents mentioned above have such a problem that the rank of the drive pulse may be moved downward to a drive pulse which causes the non-rotating state, and hence the delay might be resulted when the erroneous determination is occurred, whereby the function as the timepiece is impaired.
More specifically, the induced voltage induced between the detection segments generally tends to cause a delay in time of generation of the detection signal when the reserved drive capacity is reduced. Depending on the variations in parts or the fluctuations in load, even though the reserved drive capacity of one of the polarities is reduced, the output reserved drive capacity remains in the other polarity, which might cause a difficulty in discrimination from the drive with a reserved capacity.
In this case, it is determined to be the drive with a reserved capacity, and the main drive pulse is changed to a main drive pulse having smaller drive energy. However, there might be a case in which the output in one of the polarities has no reserved capacity with this changed main drive pulse, and hence the rotation might be disabled.
Also, in the corrective drive system in the related art, since the drive is performed with the main drive pulse having a minimum energy, there is such a problem that the rotor is brought into the non-rotation state with the minimum drive pulse after having moved downward in rank and, if the erroneous determination in detection of rotation is occurred at this time, the delay is resulted and the function as the timepiece is impaired.
According to the electronic timepiece disclosed in Patent Document JP-B-8-33457, the rotating state is determined by detecting the rotating stat of the stepping motor in a plurality of detection segments (first segment and second segment). The determination of the rotation is achieved by detecting the rotating state by the detection signal generated when being driven with the drive pulse, and the first segment is a segment for detecting the rotating state by the detection signal of one of the polarities, and the second segment is a segment for detecting the rotating state by the detection signal of the other polarity on the basis of the result of determination in the first segment. In this manner, since the detection is made in only one segment with each polarity, there is such a problem that the accuracy of determination is low, and there is a risk of moving the rank of the main drive pulse erroneously downward to a main drive pulse having a potential to cause the non-rotating state. Also, since the detection is made with one drive pulse for each polarity, there is such a problem that the determination of the rotation is complicated, and the scale of the circuit is disadvantageously increased.